An androgen-dependent, prostate-specific protein (Prostatic Binding Protein; PBP) was isolated from rat ventral prostate cytosol and antiserum against it was prepared in rabbits. Studies revealed that PBP is present specifically in the epithelial cell fraction of primary cell cultures from prostate. Fibroblast-like cells contain no PBP. Therefore, PBP is an excellent marker for identification of prostate epithelial cells. The synthesis and secretion of PBP by prostate epithelial cells in primary cultures was monitored by labeling with (35S)methionine, reaction with anti-PBP serum and precipitation of the immune complex with Staphylococcus aureus containing Protein A. Cultured epithelial cells synthesize and secrete significant levels of (35S)PBP for up to 7 days in culture. The rate of synthesis is highest on day 1 and decreases daily during the 7 day period. Synthesis and secretion of polyamines were studied as a potential marker of function of prostate epithelial cells. Polyamines were labeled with (3H) ornithine from the culture medium and then isolated by ion exchange chromatography. The (3H)polyamines were derivatized and the spermidine (SD), spermine (SP) and putrescine (PT) separated by thin layer chromatography. Individual (3H)polyamines were quantitated in cells and medium. Appearance of total (3H)polyamines in the medium peaks on day 6 of culture. The bulk of polyamines secreted into the medium and in cell extracts is putrescine. However, the SD plus SP:PT ratio peaks on day 2 of culture and declines rapidly. Fibroblast-like cells secrete a very low ratio of SD plus SP:PT. We propose that a high ratio of SD plus SP:PT in the culture medium is indicative of prostate epithelial cell function.